It is now customary to provide circuitry that allows the fire control system of a gun to remotely select the fuze operating mode as, for example, either point detonation, or point detonation delay, or air burst through the use of a timing or turn-counter device, or proximity operating modes, or any combination thereof, after the ammunition is loaded into the gun and before it is fired.
Although the invention described herein is generally applicable to medium-calibre and large-calibre tank and artillery guns, the specific application cited will be that for the 105 mm tank gun. Further, although the invention is described in respect to setting a fuze, the invention could also be used to activate a trigger for programming a camera, activating a chemical sensor, turning-on a target designator-illuminator or actuating other similar types of payload.
Currently there are two general types of ammunition carried by tanks with 105 mm guns: (1) those containing armour piercing, fin stabilized, discarding sabot (APFSDS) projectiles: and (2) those containing a high explosive (HE) fill. The former is a kinetic energy penetrator that is effective against tanks or other “hard” targets, whereas the latter's explosive fill detonates upon impact against such targets as field fortifications, light vehicles, light structures, and personnel. The separate formats of this current technology reduce flexibility and severely limit the types of targets that a tank can effectively engage rapidly.
This lack of flexibility also makes tanks vulnerable to attack from, for example, an infantryman armed with a shoulder-fired rocket-propelled grenade (RPG) launcher, if they are loaded with APFSDS cartridges. In this scenario, the tank commander would want to bring anti-personnel fire to bear as quickly as possible in the form of an air-burst projectile near the attacker to eliminate the threat to his vehicle. This is not possible with the limited choice of discrete ammunition now available for tanks carrying 105 mm guns. The same situation would apply should such a tank come under sudden air attack from a helicopter. Without an air burst capability at its disposal, defence against such an attack is compromised, nor can effective offensive action be taken against “soft” targets such as helicopters, light aircraft or lightly protected personnel.
A solution to this dilemma is to have a third type of 105 mm cartridge, one with a multipurpose capability added to the mix of cartridges carried in tanks such as the Leopard Main Battle Tank. The projectile for such a cartridge would contain an explosive charge and a multi-option fuze that is governed by a suitable fire control system (FCS) that instantaneously and remotely selects the required fuze setting of a chambered round in response to a perceived threat. Options for the fuze would include, for example, point detonation (PD), point detonation delay (PDD), proximity airburst, and timed airburst. Changes to the setting of the fuze could be made up to the moment the projectile is fired. Once accepted into the inventory, this multipurpose high-explosive projectile (MPHE) could, in most instances, replace the current HE rounds, thereby enhancing both the offensive and defensive capabilities of the tank while maintaining just two natures of ammunition on board.
Since the multi-option fuze in a MPHE projectile is to be remotely programmable by the Fire Control System when the cartridge is chambered, it must be electronic in nature. One way to achieve this is to provide a gun chamber with a specific hard-wired electrical circuit connecting the FCS to the electronic fuze. However, the existence of large numbers of 105 mm tank guns in the inventories of many armies makes it impractical to require burdensome modifications to all of them for new, hard wired circuitry. Thus, it is imperative that no modifications be made to the tank guns that will fire MPHE cartridges.
There are several ways to effect hard wiring between the FCS and the fuze. These include making the electrical contact between the FCS and the cartridge through: (1) the side of the projectile; (2) the side of the case; (3) the base of the case; (4) the primer via the firing pin; or (5) an insulated sheath containing a conductive layer. If there are to be no modifications to the tank gun, it is most practical to utilize the existing firing pin as the interface with the chambered cartridge (i.e., through direct contact with the cartridge primer). Under these circumstances, both the electrical fuze-setting signal and the electrical firing impulse enter the cartridge through a common electrical contact.
It is, therefore, imperative that the design of the fuze-setting circuit inside the cartridge be capable of carrying the setting signal to the fuze, which can be located in either the base or in the nose of the projectile, at any time up to the moment of firing without prematurely igniting the propelling charge. Such premature ignition is normally avoided by the inclusion of one or more blocking diodes, plus the fact that different signal levels are used for fuze setting and firing.
Technology to achieve this is well known and described abundantly in the prior art going back at least as far as U.S. Pat. No. 3,814,017 (now expired).
This prior art also describes a variety of novel solutions for the electromechanical circuitry to physically achieve the remote programming of a chambered cartridge prior to firing (e.g., the placement of conductors, the type of conductors, the contacts between various parts of the circuit). Each of these solutions depends on the physical design of the gun/ammunition system under consideration. Common to all solutions, however, is the requirement for reliable circuitry from the base of the case through the length of the case to the projectile, and then onwards to the nose of the projectile where the multi-option fuze is usually located. The range of solutions in the prior art is illustrated in the six patents discussed in the following paragraphs.
U.S. Pat. No. 3,814,017 shows a design with a similar intent to that of the invention. Specifically, it describes a “method and system arrangement for determining the type and condition of ammunition which is ready for firing and can be detonated electrically . . . ”. This patent, however, which has now expired, does not give details as to how the various circuits are physically located inside the cartridge. It only shows a wire running from the base of the ignition primer through the middle of the propellant charge before directly entering the projectile through a large undefined aperture, which does not appear to separate the propellant from the projectile in an airtight manner. There is no tracer in the projectile and little detail of the various electrical connections is provided beyond the written description that they are “plug contacts”. The present invention concentrates on a specific method, different from and more detailed than that described in U.S. Pat. No. 3,814,017, for installing the circuitry in the cartridge.
U.S. Pat. No. 4,015,531, which has also expired, describes a system wherein the gun voltage for initiating the primer of a round of ammunition having a fuzed warhead is used to “contemporaneously charge the power supply capacitor of the warhead”. Although this patent is primarily directed towards high rate-of-fire cannons in airplanes, the general method for transmitting the signal to the capacitor in the projectile is similar to that of U.S. Pat. No. 3,814,017 detailed in the previous paragraph. Again, the present invention concentrates on the method of constructing the circuitry, which is different from the method described in U.S. Pat. No. 4,015,531 and resolves problems encountered in the larger cartridges associated with tank guns.
U.S. Pat. No. 5,078,051 is directed “to an improved electrical communication system which facilitates the transmission of pre-launch communication from the firing mission computer to update the program of the round”, including the projectile control system. Its cartridge is similar to that in the present invention in that it contains a primer flash tube for ignition of the propelling charge through which a conductor in the form of a wire passes before exiting near the base of the projectile and continuing outside the projectile before reentering it in an undetermined way. This part of the circuit in the present invention is entirely contained inside the length of the 105 mm projectile, after entering it through a different path which is one feature of the invention.
U.S. Pat. No. 5,097,765 describes a remotely set digital time base fuze in a cartridge case where fuze power, time setting information and cartridge firing are performed sequentially over the same hardwire line through the electric primer terminal. In particular, the digital time fuze is adjacent to the base of the projectile.
U.S. Pat. No. 5,147,973 follows on from U.S. Pat. No. 5,097,765 referenced above. It, too, describes a multi-functional fuze system with overall performance objects similar to those described in the present invention. In this instance there are two fuzes, one of which is essentially identical to that described in U.S. Pat. No. 5,097,765 while the other is an independently powered proximity fuze located in the nose of the projectile.
U.S. Pat. No. 6,526,892 describes a hard-wired, remotely programmable fuze system for tank ammunition, but it necessitates modifications to the tank gun. The electrical connection with the tank in this design is through the base of the cartridge case, but it requires a connecting pin and associated circuitry as new, additional components to the gun (i.e., existing guns would have to be modified to fire the cartridge of U.S. Pat. No. 6,526,892). In this design, entry of the circuit into the projectile is at its base, but not through the tracer. Further refinements to this design are found in US Patent Application Publication 2004/0003746 A1 (8 Jan. 2004).
Details of Prior Art Electromechanical Circuits
To establish differentiation of the invention from the prior art, it is first necessary to take a closer look at three of the inventions mentioned in Section I above. FIGS. 1, 2 and 3 show the prior art configurations for the remote programming of a nose fuze in a large calibre shell for firing from, for example, a tank. They correspond, respectively, to U.S. Pat. Nos. 3,814,017, 5,078,051 and 6,526,892. These patents illustrate three different circuit configurations for transmitting the desired signals from a remote fire control system to a programmable fuze located in the nose of a chambered high explosive ammunition round.
In FIG. 1 (prior art U.S. Pat. No. 3,814,017) chamber I of large calibre barrel 2 contains shell 3 comprising cartridge case 4 and high explosive projectile 5 which contains fuze 6. Fire control system 7 is hard wired to shell 3 via conductor 8, which is connected to shell 3 through contact 9 (in breech block 10) and contact 11 (in electrical ignition primer 12). Signals from the fire control system destined for fuze 6 are prevented from entering the circuitry 13, associated with electrical ignition primer 12, by directing diodes, thereby bypassing said circuitry 13 and going onward to fuze 6 via conductor 14 and aperture 15 through the base 16 of projectile 5. The circuit is completed through the metal portion of projectile body 5 and the metal cartridge case 4, which are attached at joint 17.
In FIG. 2 (prior art U.S. Pat. No. 5,078,051) large calibre cartridge 20 comprises case 21 and fin stabilized high explosive projectile 22 contained in discarding sabot 23. Fire control box 24 is hard wired to cartridge 20 via conductor 25 and conductive ignition electrode 26, which is contained in primer housing 27. Transmission line 28 connects conductive ignition electrode 26 with fuze electronics package 29 contained in nose cone 30 of projectile 22. En route to electronics package 29, transmission line 28 first passes through the interior of primer flash tube 31 before exiting through one of the holes 32 at its forward end to bypass fins 33 of projectile 22. Transmission line 28 next enters projectile 22 in an undefined way at the tapered rear end 34 of that portion of projectile 22 that contains explosive charge 35 and then continues on through said explosive charge 35 until it reaches electronics package 29 in nose cone 30. Transmission line 28 contains the necessary conductors to transmit signals from fire control box 24 to electronics package 29 in a fully self-contained manner (i.e., it does not require the case 21 or projectile 22 or discarding sabot 23 to be part of the circuit). As in prior art U.S. Pat. No. 3,814,017 described above, signals destined for electronics package 29 are prevented from entering circuitry (not shown) located near conductive ignition electrode 26 that is reserved for the electrical ignition of primer flash tube 31.
In FIG. 3 (prior art U.S. Pat. No. 6,526,892) large calibre cartridge 49 comprises case 48 and projectile 78 accommodating tracer unit 96 and programmable projectile fuze 79. The case 48 is made up of two parts, base 77 and combustible jacket 36. Primer flash tube 37 is connected with base 77 and has an intricately designed contact plug 38 at its forward end. Contact plug 38 receives cable 39 after said cable 39 passes through primer flash tube 37, having entered cartridge 49 through annular aperture 40 of base 77. Aperture 40 is sufficiently offset from the centre of base 77 so that cable 39 is independent of primer electrode 41 (i.e., the electrical ignition circuit (not shown) and the circuit to program fuze 79 are completely different and separate); the ground for cable 39 is provided by the container 42 that holds electrode 41. Cable 39 is, therefore, effectively wired to fire control system 43, which remotely programs fuze 79. Timing cables 44 and 45 emanate from contact plug 38 and pass up the outside of the rearward end of projectile 78 so as to avoid tracer unit 96. They enter projectile 78 at aperture 46 and proceed through conduit 47 to programmable fuze 79. This design was subsequently refined as described in US Patent Application Publication 200410003746 A1 (8 Jan. 2004).
The invention described herein as follows includes features in the design of an electromechanical circuit that significantly differentiates it from the prior art described above. The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification.